Born in Kowal, Casimir first married Anna, or Aldona Ona, the daughter of Grand Duke Gediminas of Lithuania. The marriage produced two daughters, Cunigunde (d. 1357), who was married to Louis VI the Roman, the son of Louis IV, Holy Roman Emperor, and Elisabeth, who was married to Duke Bogislaus V of Pomerania. Aldona died in 1339, and Casimir then married Adelaide of Hesse. He divorced Adelaide in 1356, married Christina, divorced her, and while Adelaide and possibly Christina were still alive (ca. 1365), he married Hedwig of Głogów and Sagan. He had three daughters by his fourth wife, and they were still very young when he died, and regarded as of dubious legitimacy because of Casimir's bigamy. Because all of the five children he fathered with his first and fourth wife were daughters, Casimir left no lawful male heir to his throne.[citation needed]

Casimir is the only Polish king who both received and kept the title of "Great" in Polish history (Bolesław I Chrobry is also called "Great", but his title Chrobry (Valiant) is now more common). When he came to the throne, his hold on it was in danger, as even his neighbours did not recognise his title and instead called him "king of Kraków". The economy was ruined, and the kingdom was depopulated and exhausted by war.

Upon his death, Casimir left a kingdom that had doubled in size (mostly through the addition of lands in modern day Ukraine, then called the Duchy of Halicz), was prosperous, wealthy, and held great prospects for the future. Although depicted as a peaceful king in children's books,[citation needed] he in fact waged many victorious wars and was readying for others just before he died. He built extensively during his reign (Wawel Castle, Orle Gniazda), and reformed the Polish army and the Polish civil and criminal law. At the Sejm in Wiślica, on 11 March 1347, he introduced salutary legal reforms to the judicial system of his kingdom. He sanctioned a codes of laws for Great and Lesser Poland, which gained for him the title of "the Polish Justinian", and founded the University of Kraków, the oldest Polish University. He organized a meeting of kings in Kraków (1364) in which he exhibited the wealth of the Polish kingdom.[citation needed]

In 1335, in the Treaty of Trentschin, Casimir relinquished "in perpetuity" his claims to Silesia. In 1355 in Buda, Casimir designated Louis I of Hungary as his successor, like his father did with Charles I of Hungary for his help against Bohemia. In exchange Casimir gained Hungarian favourable attitude, needed in disputes with the hostile Teutonic Order and Kingdom of Bohemia. We must remember that Casimir was still in his early years and having a son did not seem to be a problem for him (he already had a few bastard children). Unexpectedly Casimir left no legal son, but he tried to adopt his grandson Casimir IV, Duke of Pomerania, in his last will. This part of the testament was invalidated by Louis I of Hungary, who came to Kraków quickly after the death of Casimir and bribed the nobles with future privileges.

His second daughter, Elisabeth, Duchess of Pomerania, bore a son in 1351, Casimir IV of Pomerania. He was slated to become the heir, but did not succeed to the throne, dying childless in 1377, 7 years after King Casimir. He was the only male descendant of King Casimir who lived during his lifetime. His son-in-law Louis VI the Roman of Bavaria, Margrave and Prince-elector of Brandenburg, was considered a possible successor but was deemed ineligible as his wife, Casimir's daughter Cunigunde had died in 1357 without issue. The Polish people repulsed many raids of the Tatar-Mongols. Casimir had no legitimate sons. Apparently, he deemed his own descendants either unsuitable or too young to inherit. Thus, and in order to provide a clear line of succession and avoid dynastic uncertainty, he arranged for his nephew, King Louis I of Hungary, to be his successor in Poland. Louis was proclaimed king on Casimir's death in 1370, and Casimir's sister Elisabeth (Louis's mother) held much of the real power until her death in 1380.[citation needed]

Casimir was facetiously named "the Peasants' King". The codes of laws of Greater and Lesser Poland, he introduced an attempt to put the overwhelming superiority of the nobility to an end. During his reign all three major classes (nobility, priesthood and the bourgeoisie) were more or less counterbalanced, so that Casimir could strengthen his monarchic position. He was known for siding with the weaker, when the law did not protect them from greedy nobles and clergymen. Reportedly he did even support a peasant, whose house has been demolished against his own mistress, after she ordered to pull it down, because its look disturbed her enjoyment of the beautiful landscape.

King Casimir was favorably disposed toward Jews. On 9 October 1334, he confirmed the privileges granted to Jewish Poles in 1264 by Bolesław V the Chaste. Under penalty of death, he prohibited the kidnapping of Jewish children for the purpose of enforced Christianbaptism. He inflicted heavy punishment for the desecration of Jewish cemeteries. Although Jews had lived in Poland since before the reign of King Casimir, he allowed them to settle in Poland in great numbers and protected them as people of the king.[2]

Casimir effectively divorced Adelaide and married his mistress Christina Rokiczana, the widow of Miklusz Rokiczani, a wealthy merchant. Her own origins are unknown. Following the death of her first husband she had entered the court of Bohemia in Prague as a lady-in-waiting. Casimir brought her with him from Prague and convinced the abbot of the Benedictineabbey of Tyniec to marry them. The marriage was held in a secret ceremony but soon became known. Queen Adelaide renounced it as bigamous and returned to Hesse without permission. Casimir continued living with Christine despite complaints by Pope Innocent VI on behalf of Queen Adelaide. The marriage lasted until 1363–64 when Casimir again declared himself divorced. They had no children.[citation needed]

With Adelaide still alive and Christine possibly surviving, the marriage to Hedwig was also considered bigamous. The legitimacy of the three last daughters was disputed. Casimir managed to have Anne and Cunigunde legitimated by Pope Urban V on 5 December 1369. Hedwig the younger was legitimated by Pope Gregory XI on 11 October 1371.[citation needed]

^"In Poland, a Jewish Revival Thrives—Minus Jews". New York Times. 12 July 2007. Probably about 70 percent of the world's European Jews, or Ashkenazi, can trace their ancestry to Poland — thanks to a 14th-century king, Casimir III, the Great, who drew Jewish settlers from across Europe with his vow to protect them as "people of the king",|accessdate= requires |url= (help)